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Production Know How

Production Know How
26
Aug

Recommendations for Sun Drying

Recommendations for Sun Drying include

1.Layer Thickness

2. Mixing

3. Protection

4. Additional factors affecting the drying rate

File Courtesy: 
http://www.ikisan.com/CropSpecific/Eng/links/ap_riceDrying.shtml
26
Aug

Technology options to improve Sun drying

1. Sun drying will be in practice (vogue) as long as

there is a market for low quality paddy, because it is the cheapest drying method.

2. As long as there is no quality-incentive for better quality rice it will be the preferred method whenever the weather allows. Traditional sun drying can be improved using simple tools and monitoring equipment.

File Courtesy: 
http://www.knowledgebank.irri.org/rkb/index.php/paddy-dryingmethods/sun-drying
26
Aug

Pavement drying

1. It is useful for medium to large scale

farmers, traders and millers.

2. Place threshed grain on pavements made specifically for drying. Mixing and collecting can be partially mechanization. Due to large size, labour can be more effectively used.

3. System can be improved by using pavements with elevations for the grains and drainage channels for rainwater.

4. Usually manual tools are used for mixing and grain collection

File Courtesy: 
http://www.fao.org/teca/content/rice-sun-drying-method
26
Aug

Drying on nets mats or canvas

1. It is useful for small to medium scale

farmers and also has multiple uses.

2. The drying of the grains on the mats and plastic sheets is the most hygienic method and that allows quick collection and mixing.

3. Paddy when dried on mats or canvas does not contain stones and other dirt, often found in paddy that was dried on roads.

File Courtesy: 
http://www.fao.org/teca/content/rice-sun-drying-method
25
Aug

Panicle drying

1. Drying of paddy grains that are still attached

to the panicles is a traditional method for drying small amounts of paddy.

2. The panicles are harvested with a small knife, bound together and carried to the drying location.

3. The dried panicles are then stored in farmers’ houses, for example by hanging them under the roof for protection from rodents.

4.For drying, the tied bundles are placed on pavements or mats or hung from frames.

File Courtesy: 
http://www.knowledgebank.irri.org/rkb/index.php/paddy-drying-m ethods/sun-drying
25
Aug

Options of sun drying

Options of sun drying include 

1.Panicle drying

2.Drying on nets

3.Mats or canvas

4. Pavement drying

File Courtesy: 
http://www.knowledgebank.irri.org/rkb/index.php/paddy-drying-methods/sun-drying
25
Aug

The limitations of sun drying

Limitations of Sun Drying: 

1.There is uncontrollable non-uniform drying which result in sun checks or cracks in kernels. Due to this when dried grains milled, give larger quantity of broken grains.

2. This process is dependent on availability of sun energy normally which is not available in monsoon season.

3. Large number of unskilled labours is required with no mechanical energy.

4. During the process quantity of 1 to 2 per cent of paddy is lost due to birds, insects, rats and other rodents.

File Courtesy: 
http://www.indiaagronet.com/indiaagronet/post_harvest/CONTENTS/rice.htm
25
Aug

Why Sun drying?

1. The cost of drying per tonne of paddy is relatively low as compared to mechanical drying as it requires no fuel or mechanical energy.

2. The rate of drying in the sun depends upon solar insulation, moisture content of paddy.

3. The time required for sun drying depends on the weather.

4. Size of the floor or mat required for drying is determined by matching the drying rate with the amount of paddy grains to be dried.

5. Sun drying is environment friendly.

File Courtesy: 
http://books.google.co.in
25
Aug

Sun drying

1. Sun drying is the most preferred method in India.

2. In this method spread the grains in thin layers on the floor, mix the grains for every 30 minutes and monitor the grain temperature.

File Courtesy: 
http://www.fao.org/teca/content/rice-paddy-drying-systems
25
Aug

Field drying

1. The crop is harvested at higher moisture

content and is left in the field or on bounds of field till it has dried to proper moisture content.

2. Another improved method followed in Japan is to dry harvested crop on racks. There the harvested plants are found in a bundle near the ears and are hung on a rope exposing the ears to the sun.

File Courtesy: 
http://www.indiaagronet.com/indiaagronet/post_harvest/CONTENTS/rice.htm
25
Aug

Drying Methods

In India, three methods are used for drying the paddy grains namely:

1.Sun drying

2.Mechanical drying

3.Chemical drying

File Courtesy: 
http://www.indiaagronet.com/indiaagronet/post_harvest/CONTENTS/rice.htm
25
Aug

Tempering

1. When the drying of grain is temporarily stopped the moisture within the grain equalizes due to diffusion.

2. When drying is restarted, the drying rate becomes higher compared to continuous drying. The process of stopping intermittently is called tempering.

3. In addition during tempering the moisture differences between grains equalize.

4. Tempering therefore also ensures that moisture gradients in the grain bulk that develop during drying in certain dryer types are minimized.

File Courtesy: 
http://www.knowledgebank.irri.org/rkb/index.php/drying-basics/the-drying-process
25
Aug

Uniform Drying

1. During the drying process there is always variability in moisture content of individual grains.

2. Especially in fixed-bed dryers the grains at the air inlet dry faster than at the air outlet resulting in a moisture gradient in the grain bulk at the end of the drying process.

3. For production of good quality grain or seed, this variability should be kept as low as possible.

File Courtesy: 
http://www.knowledgebank.irri.org/rkb/index.php/drying-basics/the-drying-process
25
Aug

Drying Rate/Temperature

1. Above 18 % moisture content, the grain drying rate can be increased by providing a higher temperature or more drying air without major changes in grain temperature.  

2. Below 18 % moisture content, increase in drying air temperature will not increase the drying rate but will increase grain temperatures and potentially damage the grain.

3. Therefore, higher drying air temperatures can be used to dry grain quickly down to 18% moisture content but lower temperatures should be used to remove internal moisture from the grain.

File Courtesy: 
http://www.knowledgebank.irri.org/rkb/index.php/drying-basics/the-drying-process
25
Aug

Falling rate period

1. As time passes, it takes more time for internal moisture to appear at the surface, and evaporation of water is no longer constant in time.

2. As a result, drying rate will decline, and some of the heat from the drying air will heat up the grain. 

3. For paddy grain, the falling-rate period typically occurs at around 18% grain moisture content.

File Courtesy: 
http://www.knowledgebank.irri.org/rkb/index.php/drying-basics/the-drying-process
25
Aug

Constant rate period

1. Once the grain is at the drying temperature, water starts to evaporate from the surface of the grain.

2.  During this period, all the heat from the drying air is used to evaporate surface moisture and the amount of moisture removed from the grain is constant in time.

3.  It is therefore called the constant-rate period. During this period, grain temperature is constant as well.

File Courtesy: 
http://www.knowledgebank.irri.org/rkb/index.php/drying-basics/the-drying-process
25
Aug

Pre-heating period

1. When wet grain is exposed to hot air, initially only a very slight change in moisture content is observed.

2. This happens because all the heat provided in the drying air is used to heat up the grain to the drying temperature.

 

File Courtesy: 
http://www.knowledgebank.irri.org/rkb/index.php/drying-basics/the-drying-process
25
Aug

The drying process - Moisture Removal

1. In paddy grain, moisture is present at two places: at the surface of the grain, ‘surface moisture’, and inside the kernel, ‘internal moisture’. 

2. Surface moisture will readily evaporate when grain is exposed to hot air.  Internal moisture evaporates much slower because it first has to move from the kernel to the outside surface.

3. As a result, surface moisture and internal moisture evaporate at a different rate.  This difference results in a different ‘drying rates’ for different period of drying.

File Courtesy: 
http://www.knowledgebank.irri.org/rkb/index.php/drying-basics/the-drying-process
25
Aug

Equilibrium Relative Humidity

1. If the grain is stored in an enclosed storage environment, the air surrounding the grain if it is well sealed is not in free contact with outside air. 

2. In this case, the relative humidity of the enclosed air will reach equilibrium with the moisture content in the grain.  The final relative humidity of the enclosed air is often expressed by the ‘equilibrium relative humidity’.

File Courtesy: 
http://www.knowledgebank.irri.org/rkb/index.php/drying-basics/equilib rium-moisture-content
25
Aug

Equilibrium Moisture Content

1. The stored grain moisture content will be generally influenced by the temperature and relative humidity of the surrounding environment.

2. Protecting the grain during rainy season when there is high relative humidity in the air is very important it will leads to the grain quality deterioration. 

3. The grain moisture content of paddy stored in jute bags or clay pots will automatically increase in the rainy season to unsafe levels regardless of how well the grain was dried before storage.  

File Courtesy: 
http://www.edwardsgroup.ca/keho/keyconcepts.cfm?local=KeyConcepts
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